Medical electrodes are used to connect medical electronic equipment, such as medical stimulation equipment, to patients. Stimulation electrodes are affixed to a patient's skin and connected by an electrode lead to an appropriate piece of medical equipment. Electric current generated by the medical equipment is applied to the patient via the electrode. In order to better understand the problems presented by the prior art, and solved by the present invention, a brief discussion of the technological progression of recent years from reusable electrodes to disposable electrodes is presented.
Typically, reusable electrodes were used in conjunction with a separately applied wet gel or paste. The wet gel offered improved adhesive and conductive properties at the point of contact between the electrode and the patient's skin. After the electrode was removed from the patient, both the electrode and the patient's skin had to be cleaned of any gel residue. The reusable electrode was then ready for use with the next patient, after which, the above cleaning process was repeated. Thus, sanitation of the electrodes, personal hygiene, and the mess of the wet gels were problems associated with the reusable electrodes.
The disposable stimulation electrodes used in the prior art were developed to overcome the aforementioned problems. The benefit of such disposable electrodes was that they could be discarded after the first use. Thus, the concerns of sanitation and personal hygiene that existed with reusable electrodes were reduced by using the disposable electrodes. However, many of the disposable electrodes continued to use the wet gels described above. Thus, the mess associated with the wet gels persisted. Eventually, the wet conductive gels that were used with the reusable electrodes gave way to dry conductive gels that formed a part of the disposable electrodes. Typically, the dry gels of the prior art electrodes were not as messy as the wet gels and, therefore, were more convenient to use. However, the dry gels have presented their own problems such as: short shelf life; poor adhesion properties; lack of flexibility; and, patient discomfort during periods of prolonged wear. These problems are discussed in more detail below.
Previous attempts to develop disposable electrodes using dry conductive gels have typically resulted in electrodes that are either too rigid to readily conform to the body contours or have low surface tack properties. As a result, such electrodes tend to fall off patients during periods of extended wear. Another problem associated with disposable electrodes has been their limited shelf life. Corrosion between the electrode plate and the electrolyte used in the dry gel has limited the typical shelf life of disposable electrodes to between six months and one year.
Yet another problem is the nonuniform current density profile associated with the prior art disposable electrodes. Typically, the electric current at the edge of the conductive gel is substantially greater than the electric current near the center of the conductive gel. This unequal current distribution within the gel causes the gel to have a high current density near the edge of the gel. During prolonged periods of repeated stimulation, the high current density causes general discomfort to the patient and potential burning of the patient's skin near the edge of the gel.
As will be readily appreciated from the foregoing discussion, there is a need for a disposable electrode that: remains adhered to the patient's skin for extended periods of time; has a long shelf life; is convenient to use; and offers improved current density thereby reducing patient discomfort and burning during prolonged periods of repeated stimulation. Additionally, such an electrode should be easily and inexpensively manufacturable.